High-Resolution Millimeter-Wave Tomography System for Characterization of Low-Permittivity Materials

Tomographic microwave imaging is employed in numerous industrial applications, e.g., nondestructive testing. However, most existing systems are not suitable for measurements of low-permittivity materials such as gaseous substances or insulating foam with high air content. This paper introduces a 79 GHz high-resolution tomography system enabling characterization of materials with relative permittivity close to one. It is based on fully-integrated frequency-modulated continuous-wave radar transceivers which significantly reduce cost and complexity. A first prototype is built with two radar sensors and a rotary stage to emulate a higher sensor count. The medium-dependent time-of-flight through the area-under-test is evaluated and Tikhonov regularization is applied to solve the inverse problem and reconstruct a 2D image. System simulations and measurements with low-permittivity foam objects confirm the feasibility of this approach.